Marina Iosifovna Kondrashkina

The spatial variability of the content of granulometric fraction d > 0,25 mm in the arable layer of soddy-podzolic cultivated soil on an area of 18 hectares was studied. The soil formed in the loess-like loam, underlain by moraine deposits. Samples were taken from the upper (0–10 cm) and lower parts of the arable layer (10–20 cm) following a random-stratified sampling scheme. The total number of samples was 350 cores. The average fraction content was about 22%, the coefficient of variation was 39–41%, the distributions were approximated by a logarithmically normal distribution. The Spearman correlation coefficient between values at different depths equaled to 0,87. The spatial distribution cartograms were constructed by the ordinary kriging method using a spherical variogram model. It is shown that preliminary censoring of high sample values (quantile 0,95) gives better results when constructing a cartogram than removing a linear spatial trend and logarithm of the original data. Spatial structures with reduced and increased values were found on the site, the average linear sizes of which was about 100 m.  Presumably, they were associated with the heterogeneity of soil-forming material.

Using the example of data from the article by E.A. Dmitriev et al., the estimation of the required number of soil samples to assess the SOC content in the forest biogeocenosis during monitoring studies is considered. Primary data on SOC content were obtained in the spruce forest at 166 points in layers 0–10, 10–20, and 20–30 cm after removal of the litter. The sampling was carried out at the nodes of a regular grid of equilateral triangles with 1 m side within a regular hexagon with a side of 7 m. The SOC content was determined by the Tyurin method. The original article presents statistics for three zones — near-stem, under-crown and inter-crown space. Spatial variation in all zones and at all depths is high, the coefficients of variation are about 50%. It is shown that the number of replicates required for estimating the average SOC content at a 95% confidence level in the 0–10 cm layer is hundreds of samples and decreases to tens of samples in the 20–30 cm layer. Since the number of repetitions for testing hypotheses about the equality of means depends not only on the confidence level, but also on the power of the criterion used, the required number of repetitions increases several times. Sampling with samples taken from the entire vertical layer of 0–30 cm and forming mixed samples from them reduces the number of required repetitions, however, careful observance of sample preparation, including primary mixing of samples, is required.

The ongoing work on forecasting changes in soil carbon reserves using various mathematical models requires primary data for different points in time. The paper examines archival results of observations of intra-seasonal carbon dynamics obtained in 1983 on arable sod-podzolic soils in Educational and Experimental Soil and Ecological Center of Lomonosov Moscow State University "Chashnikovo". Measurements were carried out from June to September on 30×30 m plots located in three crop rotation fields. Samples were taken from layers 0‒10 and 10‒20 of the arable horizon. The number of measurements in each period on each field was 25. After preliminary rejection of the results that did not meet the hypothesis of homogeneity of the soil horizon, the data were processed by ANOVA. It is shown that in the arable horizon (0–20 cm layer) the range of intra-seasonal variability of carbon content can be about 0.10%. Minimum values of carbon content were observed in August-September.

The carbon reserves in main components of Moscow region coniferous-broadleaf forest were studied: various fractions of the tree stand, dead wood, mortmass, litter, living ground cover and mineral profile of the soil. To assess the potential intensity of organic matter decomposition, a number of indicators of the functioning of the microbial biomass were determined. An assessment is given of the carbon reserves and their shares in the ecosystem components that differ in the rate of renewal and potential capacity for carbon sequestration, as well as the degree of their spatial variation. The total carbon pool of the studied forest ecosystem is 18.7+0.8 kg·m–2, with almost 90% of the total stock concentrated in the perennial parts of the tree stand, dead wood, mortmass and mineral profile of the soil. These most stable pools are characterized by the least spatial variation within the biogeocenosis. The carbon reserves of the assimilating part of the grass layer and tree leaves are only 0.02 and 0.08 kg·m–2, respectively. The carbon reserves of litter are quite low - 0.21 ± 0.04 kg·m–2, which does not exceed 2% of the total carbon reserves of the ecosystem. The data obtained indicate that even secondary subclimax forest ecosystems are a significant absorber of atmospheric carbon, mainly due to the mass of the tree stand and soil organic matter.